1. Field of the Invention
This invention relates generally to electronic sweep generating circuits. In particular, this invention relates to an electronic sweep generating circuit for producing a sawtooth waveform signal to be utilized by a helmet mounted display system.
2. Description of the Prior Art
Sweep generators for providing a sawtooth waveform signal to drive the scanning coils of a cathode ray tube or the like are well known in the prior art. The sawtooth waveform signal produced by such sweep generators is generally synchronized with an input sync signal so as to provide at the output thereof a ramp voltage having a constant slope or a constant peak.
Prior art sweep generators customarily generate sawtooth waveform signals by charging a sweep capacitor at a uniform rate and then discharging the capacitor in synchronism with an input sync signal. A controllable current source supplies charge to the sweep capacitor to provide the ramp voltage. The ramp voltage is continuously integrated and compared with a reference voltage and the difference between the integrated sweep voltage and the reference voltage is used to control the current source.
These sweep generators of the prior art, while satisfactory for their intended purpose of producing a sawtooth waveform signal to drive the scanning coils of a cathode ray tube, have some inherent shortcomings. In particular, the aforementioned sweep generators are either limited to a narrow range of input frequencies or limited to a very slow response time. In addition, such sweep generators of the prior art have been found unsatisfactory for use in a helmet mounted display system or the like which displays for a trainee pilot a visual image upon a retroreflective display screen.